Concrete will have control joint cracks, or it will crack. It is not "seamless". Or, you could do sheet vinyl.

I misspoke: we don't want the lines associated with tile. Concrete cracks are no problem. I'll definitely look into these ideas. Thanks. Any other suggestions appreciated.

If cracks in porous stainable concrete aren't an issue to you, then grout joints in a 24"x24" tile floor ought not to be an issue either. And porcelain wears so much better.

A "seamless" look is going to be possible only with concrete or epoxy. Everything else has seams - including sheet vinyl or lino. Stiffen the subfloor, add concrete topping and then finish. This is the only way you will get the concrete look that is "seamless" and in the esthetic you want. But they will still throw in control joints that will look like "seams".

An epoxy professional MIGHT be able to do something to regular plywood - but the cost would be "off-putting".

Porcelain tile will also require reinforcing the subfloor. There are large format vinyl tiles that can get the look you want. Sheet vinyl might have it.

if money is no object, then I guess you could do terazzo, which would be relatively uniform and wear really well. (still reinforcing the structure, of course.)

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